Aerodynamic braking device



Sept. 11, 1945,. s. D. ROBINS AERODYNAMIC BRAKING DEVICE Filed May 8, 1943 2 Sheets-Sheet l INV ENTOR Jaws Jfohns J'armal Sept. 11, 1945. s n R s 2,384,640

AERODYNAMIC BRAKING DEVICE Filed May a, .1943 2 Sheets-Sheet 2 ATTO Patented Sept. 11, 1945 UNITED STATES PATENT OFFICE AER-ODYNAMIC BRAKING DEVICE Samuel Davis Robins, New York, N. Y.

Application May 8, 1943, Serial No. 486,123

'7 Claims. (Cl. 244-138) This invention relates to fluid dynamic braking devices for retarding the progress of bodies through a fluid medium and relates more particularly to aerodynamic braking devices for retarding the descent of bodies through the atmosphere.

Objects and advantages of the'invention'will beset forth in part hereinafter and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the instrumentalities and combinations pointed out in the appended claims.

The invention consists in the novel parts, constructions, arrangements, combinations and improvements herein shown and described.

The accompanying drawings, referred to herein and constituting a part hereof, illustrate various embodiments of the invention, and together with the description, serve to explain the principles of the invention.

Of the drawings:

Figure l is a view in top plan of a typical and illustrative embodiment of this invention;

Figure 2 is a view in section taken along the line 22 of Figure 1; I

Figure 3 is a fragmentary view in perspective of the embodiment of Figure 1 as applied to an object such, for example, as a package for mili tary supplies, the View depicting in diagrammatic fashion various transitional positional arrangements of the embodiment and object in rotational descent;

Figure 4 is a view in section taken along the line 4- of Figure 1;

Figure 5 is a view in end elevation of the showing in Figure 4 as viewed from the right of Figure 4;

Figures 6 and 7 are views similar to those of Figures 4 and 5, respectively, but with the stabilizer at a setting corresponding to the dotted line position of the stabilizer in Figure 1;

Figure 8 is a fragmentary view in plan, of a modified vform of lifting structure of this invention; I

Figure 9 is a view in section taken along the line 99 of Figure 8;

Figure 10 is a view in plan of anothermodified form of lifting structure of this invention;

Figure 11 is a view in side elevation of the lifting structure shown in Figure 10, in a folded condition; and

Figure 12 is a view in perspective of the lifting structure shown in Figure 10, in a launching container and as applied to an object to be parachuted.

Objects of this invention are: to provide a new and useful fluid dynamic braking device for retarding the progress of bodies through a fluid medium; to provide a new and useful parachute device which will develop a retarding force greater than is obtainable from other parachutes of equal weight, which will require less costly material, can be constructed at a lower cost, and will be of lighter weight than other parachutes of equal retarding capacity; which will be less visible to the eye in operation and hence offer a poorer target for enemy action, which will have a higher aerodynamic efficiency than other parachutes, which will not oscillate and spill wind as do conventional parachutes, which will have stable performance characteristics, as for instance, a uniform rate of descent regardless of gusts, air currents and the like, and will provide a greater thrust for the same weight and factor of safety than other parachutes; and, to .provide a new and improved bomb brake.

In accordance with the illustrative embodiments of my invention, there is provided an auto-stable wing, one tip of'which connectsloy an intermediate flexible link to the load tobe lowered. By the term auto stable wing is meant a wing which will meet the air at an angleof-attack, preferably constant, within thedesired range of angles-of-attack; This combination, I have discovered, will almost instantly spin when rapidly passing through a fluid medium around an axis which lies in the path of the initial motion or is tangent to the path of motion should it be curved. For example, if the load be dropped vertically, the spin axis will be vertical; if the load be ejected from a horizontally moving airplane, the spin axis will be horizontal, and will gradually become more vertical as the path of motion becomes more vertical under the gravitational influence.

The wing, airfoil, or blade, if connected to the load only by a cable or other suitable flexible intermediate link, may occupy any position whatever with respect to the load and the airflow direction, when first released. But I have found that no matter what this random attitude may be at first, the spinning about the axis above described occurs almost instantly.

As will be brought out more fully hereinafter, the directional sense of rotation may be either or only clockwise or counter-clockwise, depending upon the characteristics of the wing in flight.

Through the provision of the combination a predetermined value. the wing atany coning angle is held to a safe above described, a wing of given weight can lower an object (load) more than twenty times as heavy at a vertical rate of only twenty feet per second (about fourteen miles per hour) which is usual parachute sinking speed. Such a ratio between supporting structure and useful load has no known precedent in any known form of glider, parachute or aircraft. Moreover, the high aerodynamic efliciency of my device is further evidenced by the relationship between total weight, blade area, and sinking speed since, for example, a total weight of thirty-three pounds supported by a wing or blade of only one square foot area will descend at a speed twenty-two feet per second.

of approximately maximum and with it the retarding force is safely limited. The requisite decrease in R. P. M. is preferably obtained by automatically varying the stabilizer setting, and hence the angle of attack of the wing in response to the spanwise component of centrifugal force in excess of a predetermined value. In this connection it may be noted that for a given axial thrust (retarding force) the highest accompanying blade speed will occur at the angle-of-attack of highest L/D for the whole device. Therefore whether the angleof-attack be increased above the value of L/D maximum or decreased below said value, a re- The wing or airfoil structure is made .autostable about its span-wise axis (usually referred to as the Y-axis). required to provide stability about the X and Z axes because centrifugal force and lift powerfully locate the blade with respect to these axes.

Stability of the wing about its Y axis, longitudinal stability, is accomplished just as in the airplane, by balancing the wing moment against a stabilizer moment in such a way that any departure from the chosen stable angle-of-attack is accompanied by a restoring moment. The stabilizer moment is furnished by stabilizer means of suitable area which may be integral with or separate from the wing. I

Airplanes require longitudinal stability not only for one longitudinal C. G. location but throughout a considerable range of fore and aft locations. Hence, they require relatively large stabilizers, lo-

cated with advantageous leverage, some distance from the C. G. Since the C. G. is fixed chordwise in my device no such powerful stabilizer moments become necessary and a wider choice of stabilizing means are applicable with practicality.

Thus, stabilization can be accomplished not only a with a small trailing stabilizer, the recognized airplane type in conventional use, but by a leading or canard stabilizer. Moreover, a reflex trailing edge applied to the wing serves the purpose in the place of projecting stabilizers.

It should be understood that fora given angleof-attack on the wing,which unless the stabilizer setting be altered, will remain unchanged regardless of spinning speed and other variables, the retarding force will be proportional to the'lift force and also the centrifugal force. These three forces all vary as the square of the linear velocity.

When the load and its wing are launched in a moderate air stream, as from an airplane flying at say eighty miles per hour, the consequent spin, although at first at a higher R. P. M. than the final stable rotational speed accompanying stable rate of descent, is not excessive and will not burst the structure or its cable from undue centrifugal force. However, should thelaunching be made at say 125 miles per hour, the over spinning becomes serious and results in high centrifugal stress. Likewise, the retarding force is unnecessarily high. 1

Military use may require discharging the load at flight speeds in excess of even 125 miles per hour an also a limited moderate retarding force is desired in order not to subject the load and retarding structure to excessive forces.

Means are therefore also preferablyprovided for decreasing the R. P. and hence the centrifugal force, of the wing in response to the spanwise component of centrifugal force in excess of Thus, the R. P. M; of

No aerodynamic means are ductionof blade speed will take place.

In order to preserve the desired feature of high aspect ratio at the blade loading providing a favorable rate of descent without sacrifice of compactness as blade span is increased with increased load weight, the blade is preferably of foldable construction and so designed that any protuberances, such as the stabilizer when required, may be disposed between the overlying sections in their folded state. As has been stated, a blade loading of 32' pounds per square foot is permissible and yields a moderate rate of descent. A blade of three square feet will handle about a lb. loa and such a blade is not large. But because of the desirability of high aspect ratio, such a blade should have a chord of about six inches and a span of about six feet. Such 'a length is not objectionable in flight but is undesirable because preparatory to use it cannot usually be stowed against the load to be lowered and within the length dimension of said load. I have found that half the extended blade length comes short of the usual load length and makes a convenient maximum blade dimension for stowage purposes. The blade may therefore be conveniently hinged at the half span and if cle sirable, two or more such blade hinges may be provided resulting in an extremely compact folded unit. For practical purposes a single hinge meets the usual requirements. Thus, for a 100 pound load, the whole device may be packed in a container in'a rectangular space 6 x 36" by about 1 /2" providing for two blade thicknesses plus the folded stabilizer and the container fastened releasably to the load by a separable band permitting discharge of the load, container and its contents from an aircraft, as a unit. Separation of the band may be effected upon dise charge, the load in its initial free fall serving to pull the device from the container so that it may substantially immediately thereafter unfold and commence spinning as above described.

It will be understood that the foregoing general description and the following detailed description as well are exemplary and explanatory of the invention but are not restrictive thereof.

Referring now to the embodiment of the invention shown in Figures 1 to 7 inclusive, an airfoil I0 is adaptedto be connected by an intermediate member H to an object [2 constituting a load whose progress through the atmosphere is to be retarded. In Figure 3 is depicted the system thus formed which in flight rotates around a spin axis, such as the axis ra: depicted in Figure 3, constituting the thrust axis of the system.

The airfoil ID may be of any efficient contour but as here preferably embodied is a symmetrical section, such, for example, as the N. A. C. A. .0012.

The airfoil It) carries a stabilizer l3 in spaced following relation thereto, the stabilizer being mounted on an outrigger M and set at an angle to the chord of the airfoil I0, that is, at a tail angle at which it will balance the pitching moment, if any, of the airfoil III about the center-ofgravity of the auto stable airfoil-stabilizer assembly I5, at the desired stable angle-of-attack, and will provide the necessary restoring moment to return the'airfoil to the desired angle should it be deviated therefrom.

Where the main airfoil develops a positive pitching moment at the stable angle-of-attack, a lifting tail is required and vice versa. Preferably, and in accordance with well known principles of longitudinal stability of airplanes, the assembly [5 should be stabilized to meet the air at its angle of-attack of maximum L/D and the stabilizer setting and the relative locations of the center-of-gravity of the assembly and the airfoil center of pressure are preferably selected with this object in view. It should be understood, however, that the stable angle-of-attack may lie anywhere within a wide range of angles-of-attack without material variation in the rate of descent of the system in flight. In other words, the angle-of-attack is not necessarily critical although for optimum results the more efficient angles are to be preferred.

The desired chordwise location of the centerof-gravity of the assembly I5 relative to the center-of-pressure may be brought about by a suitable chordwise, distribution of mass in'the assembly I5. In the embodiment of Figure 1, the outrigger I4 extends forwardly of the leading edge of the airfoil II), the extension I6 being suitably weighted so as to fix the center-fgravity of the assembly at the desired location.

The stabilizer I3 is hingedly'mounted on the outrigger I4 in such fashion that the centrifugal force which develops as the assembly I5 rotates about the spin axis r-a: (Figure 3) will tend to alter the stabilizer tail angle and, in consequence, the stable angle-of-attack of the airfoil I0. q As here embodied, and for purposes previously stated and as best shown in Figures 4 to '7, the outrigger I4 is provided with a spring hinge I! of which one arm I8 is secured to the stabilizer I3 and the other arm I9 is secured to the outrigger.

The hinge axis Y--Y (Figure 4) of the spring hinge I1 intersectsthe stabilizer I3 ahead of its center-of-gravity, the hinge arm l8 positioning the stabilizer at the desired angle to the chord of the airfoil I0, that is, at the tail angle T (Figure 5) at which the airfoil I!) will be caused to meet the air at the desired stable angle-of-attack. Thus, centrifugal force will tend to rotate the stabilizer I3 clockwise, as viewed in Figure l, toward the dotted line position there shown. This tendency is opposed by the action of the hinge spring 20 which is suitably loaded'to resist such movement until the centrifugal force reaches a predetermined safe maximum.

In order that the clockwise movement may effeet a desired change in the tail angle of the stabilizer I3, the hinge axis YY is tilted at an angle to the span of the airfoil Ill. The tilt of the hinge axis may be either to the right or to the left from the plane of the vertical axis Z-Z, as viewed in Figure 4, depending upon whether a more positive or a more negative tail angle is desired from the movement of the stabilizer.- As here embodied and as best shown in Figures" 4 and 5, the hinge axis Y,-Y is inclined to the right of the vertical axis Z- -Z so that clockwise movement of the stabilizer, as viewed in Figure 1, toward the dotted line position will reduce the tail angle, as is depicted in Figures 6 and '7, and hence operate to reduce the angle-of-attack of the airfoil l0. Obviously the hinge axis may be inclined in the opposite direction, if desired, so that clockwise movement of the stabilizer will increase the negative tail angle and thereby operate to increase the angle-of-attack of the airfoil I0 and consequently reduce its speed, to a safe maximum. Manually operable-means, such as the set screw 22', may be provided for setting the stabilizer at itsinitial tail angle. It will be understood that as the speed of the assembly I5 decreases and the centrifugal force acting on the stabilizer I3 is reduced to a predetermined safe maximum, the spring will operate to return the stabilizer from a setting'such as is shown in Figures 6 and 7, toward its initial setting such as is shown in Figures 4 and 5, at which the airfoil I0 will meet the air at a lesser stable angle-of-attack.

The link II may be rigid or on the other hand may be extremely flexible in all senses, torsionally and otherwise. As here preferably embodied the link I I comprises a slender wire rope flexibly connected at one end to the tip of the airfoil II] as by a fitting 23. The other end of the link 'II is preferably provided with a fitting 24 by which the link may be flexibly attached to the load I2. It willbe understood that for a given peripheral speed of the assembly'lfi, the stress in the link I I ,that is, the cable pull due to centrifugal force will decrease with increased length of cable. Hence, the length of the cable chosen becomes an important contributing factor in establishing the operating centrifugal load.

In order to facilitate packing or stowing of the assembly l5 as a whole, means are provided for folding the outrigger I4 so'that the stabilizer may be folded over onto the airfoil I0. To this end, the outrigger is divided slightly aft of the trailing edge of the airfoil I0 into front and rear sections which are'hingedly connected by means of a spring hinge 25 at the top of the outrigger.

The sections are releasably secured at the bottom of the outrigger by latch means operative automatically to lock the sections in the extended unfolded position of the outrigger. The latch means may comprise a pair of latch members 26 one on each outrigger section which are adapted automatically to engage with each other and interlook as the sections are brought into their extended positions, as in Figure 2, through the ac tion of the spring hinge 25.

In the operation of the embodiment of the invention depicted in Figures 1 to 7 inclusive,

the load I2 is dropped from an aircraft, pulling the cable II with autostable assembly tached, after it. The dynamic forces acting on the assembly will substantially immediately set it into auto-rotation about a spin axis, such as the axis 2-1: in Figure 3, and develop a dynamic lifting force to brake the descent of the object I 2., In its transition from its initial launching attitude to a final equilibrium position, the coning angle of the system will gradually become less and pass, for example, from the high angle condition m (Figure 3) through the intermediate condition as to an equilibrium position of relatively lowconing angle as. The airfoil assembly I5 is normally stabilized to meet the air preferably at its angle-of-attack of maximum L/D. During the initial stage of descent when the kinetic energypossessed by the rotating system is relatively large, the peripheral velocity of the ,blademay be so high that stress in the cable II due to centrifugal, forcetends to develop beyond a safemaximum. The stabilizer I3 under these conditions operates to decrease the tail angle and hence the angle-of-attack of the airfoil Ill. The lowered L/D ratio at this new angle of attack operates to decrease the blade speed and the centrifugal force. As the blade reaches a safe peripheral velocity, the stabilizer |3 tends to restore the blade to the normal angle-of-attack.

In Figures 8 and 9 there is depicted a modified form of longitudinally stabilized lift-producing structure. As there embodied, an airfoil 35 is provided with an upturned trailing edge stabilizer portion 36. The airfoil 35 is adapted to be connected to theobject l2 as by the link (Figure 1) in the manner previously described. A loading member 31 may be provided which extends forwardly from the leading edge of the airfoil and is suitably weighted'so that the chordwise location of the center-of-gravity of the airfoil will be in proper relation to the center-of-pressure at the angle-of-attack influenced by the setting of the trailing edge stabilizer portion 36.

The stabilizer portion 36 is preferably hinged on a, spanwise axis 38 and forms a stabilizer member by which the airfoil may be stabilized at any one of a number of angles-of-attack. Centrifugally responsive means are provided for automatically altering the angle-of-attack of the airfoil when the centrifugal force developed in the link reaches a predetermined safe maximum and for restoring the airfoil to its initial angle-of-attack when the centrifugal force has been reduced to the safe maximum by the resultant decrease in blade speed. In the embodiment of Figures 8 and 9, a lever 39 is pivotally mounted on an upright shaft 40 within the airfoil 35. The axis of the shaft 40 passes outside of the c enter-of-gravity of the lever 39 so that the effect of centrifugal force on the lever 39 as the airfoil 35 rotates about the thrust axis :rx (Figure 3) will be to cause pivotal movement in a clockwise direction, as viewed in Figure 8. The shaft 40 is surrounded by a tensioned coil spring 4| which opposes the tendency toward clockwise movement of the lever arm 39. A link 42 connects the other end of the lever 39 to a fitting 43 at the top of the stabilizer portion 36 so that clockwise movement of the lever 39 as viewed in Figure 8 will raise the stabilizer portion 36. The spring 4| prevents the lever 39 from moving until centrifugal force reaches a predetermined safe value and thus holds the stabilizer portion 36 at a normal setting. As the centrifugal force tends toincrease beyond the safe maximum, the lever 39 rotates clockwise so as to pull on the link 42 and hence lift the stabilizer portion 36 to increase the angle-of-attack the required amount and reduce the blade speed of the airfoil to the preferred condition whereupon equilibrium conditions are restored.

Referring now more particularly to the embodiment of the invention shown in Figures 10 to 12, an auto-stable, lift-producing assembly 49 is connected flexibly to the flexible link II by a fittin 54 which is preferably received within the confines of the. airfoil so as to minimize aerodynamic drag at the fitting.

The assembly 49 comprises an airfoil 50 which is of sectional construction and hinged. intermediate its tips so that it may be folded or 001- lapsed for accommodation within a smaller space so as to provide a more compact structure for stowage and attachment to the load. As, here embodied inboard and outboard sections and 52 are pin connected to an intermediate hinge section 53 along the chordwise extending hinge axes 55 and 56 respectively.

An outrigger 51 is pivotally mounted on the airfoil section 52 and is pin connected thereto by a pin58. Spring means (not shown) concentric with said pin acting between the outrigger and section 52 urge the outrigger in chordwise extending relation to the airfoil 50 against a, stop member 59.

The outrigger 51 carries at its trailing extremity a stabilizer 60 which is connected to the outrigger by a spring hinge 6|. The latter, in contrast to the spring hinge ll of the embodiment of Figure 1, has its hinge axis Y-Y (Figure 11) tilted in the opposite direction to that shown in Figure 4 so that the centrifugal force developed by the stabilizer 6|) as it rotates around the spin axis :r-xc (Figure 1) of the system, will tend to urge the stabilizer in a counterclockwise direction (as viewed in Figure 10) and increase, rather than decrease, the tail angle of the stabilizer. This increase will operate to increase the stable angle of attack of the airfoil 50. The decrease in L/D of the assembly consequent upon increasing the angle-of-attack above that of maximum L/D will operate to reduce the blade speed and reduce the centrifugal force acting in the cable H as has previously been explained. As the centrifugal force is reduced, the stabilizer 60 will tend to be returned by the action of the spring hinge to its normal position. 2

Through the provision of the intermediate section 53, the'airfoil 50 is adapted to be folded, one section upon the other into the position shown in Figure 11. Through the provision of the hinge pin 58, the outrigger 51 is adapted to rotate on the pin axis from the chordwise posit on to a spanwise extending position, the dotted line position in Figure 10, in which it lies between the sections 5| and 52 when they are folded. In order that the stabilizer 60 may be wholly contained within the space between the sections 5|, 52, the stabilizer spring hinge 6| and the outrigger 51 form the leaves of a spring hinge having the hinge pin 64. The hinge pin 64 permits movement of the stabilizer 60 from its normal operating position shown in solid lines in Figure 10, to a folded position i in substantial parallelism with the outrigger, as shown by the dotted line posi tion of the stabilizer in the same figure. Any suitable form of spring hinge connection between the outrigger 51 and the stabilizer spring hinge 6| may be utilized which will normally urge the stabilizer from the folded to the open position. A stop (not shown) which maybe formed by an extension of the outrigger 51 serves to fix the open position of the stabilizer hinge 5 I.

In order that the outrigger 51 will maintain its chordwise position in flight against the stop 59, the center-of-gravity of the outrigger with stabilizer is located forwardly of the hinge pin 58. As here embodied, the outrigger is provided with an extension 65 of sufllcient mass to position the center-of-gravity in the desired forward location.

Thus it will be seen that with the sections 5|, 52 folded one upon the other, the space therebetween is adapted to receive the outrigger 51 and other protuberances such as the stabilizer 60, and to provide a more compact structure which may be easily stowed in a small space prior to use. The

structure when opened provides a lifting structure of high aspect ratio at a blade loading providing a favorable rate of descent as blade span is increased with load weight. For example, a blade of approximately 5 inch chord and span appro imately 3 /2 feet will support a load of approximately fifty pounds at a rate of descent-of approximately 22/second and'may. be conveniently constructed in accordance with. the embodiment of Figures 10 and 11 so as to be received in a space 1.5" xx21".

Very much greater weights can be handled with proportionately larger folding blades and still retain the great compactness as just illustrated.

It will be apparent to those skilled in the art that the centrifugal force generated by the airfoil 50 in rotation about the spin axis will be sufficient to hold the sections 5|, 52 in extended spanwise relation.

The embodiment depicted in Figures -11 is particularly adapted for use with loads requiring relatively large area. Obviously, the airfoil in its folded condition prior to use may be kept together by any suitable means such as a band, a clip, or the like passing around the sections and preventing the outrigger and stabilizer from unfolding. Preferably, however the airfoil in its folded state is lodged in a disposable container "I0 of wood, metal or other suitable material dimensioned just to receive the airfoil therewithin in readily separable relation. The container not only serves to protect'the lifting structure during transit or storage but may be utilized to facilitate launching of the blade with load attached from rapidly moving aircraft. Preferably, therefore, the container or packet is contoured externally so as to conform to the shape, of the gasoline pillow, bomb, food container, packaged radio or other packaged article forming the load to be lowered and is releasably secured thereto by a strap or other means separable upon launching so as to free the container and load article from each other, and permit the blade and container to separate from each other. I

Referring now more particularly to Figure 12, a' container 10 enclosing the folded blade assembly 59 is releasably secured to a load article ll by means of a band 72 passing around the'packet thus formed. The ends of the band 72 are releasably connected to each other as by means of a locking pin 13 to which is' connected a release cord 14. The pin 13 preferably passes through an eyelet 15 anchored to the container 10 and forming a guide ensuring that the pin will be pulled substantially axially by the cord 14.

The cable II which forms a flexible link of suitable length between the blade assembly 50 and the load article H is anchored to the load article in suitable fashion as by means of the bracket 16 and may be disposed in the most convenient fashion between the band 12 and the load article I.

There is thus provided a parachute packet of compact size which may be stowed in snug fashion prior to use. For launching, the cord 14 is preferably secured to the aircraft so that when the packet is dropped, the pin I3 will be withdrawn thereby freeing the band 12 and freeing the container 10, from the load article H. The blade assembly 50 is now free to leave the container 10, the separation being effected either by wind action or by pull exerted on the blade assembly by the load article through the cable ll. As soon as the blade assembly is free of the container, the system formed by the load article, link and blade assembly will substantially immediately be set into auto-rotation about the spin axis as has previously been described. As an alternative means of limiting the cable stress the cable'may be wound' on a braked reel carried for example by the blade';=or the object, or. positioned between the two,'so that when the cable stress reaches a predetermined safe maximum, sufficient to overcome the restraining actionof the reel braking mechanism, the reel may rotate and pay out cable in amount sufficient to reduce the centrifugal force the required amount.

Although the invention has been shown as applied to braking the progress of an inanimate object through the atmosphere, it will be understood that it may be applied to animate objects. In its application to a person, it is preferredthat two or more blades-be employed so as to provide a balancedsystem. In such case each blade may be connected by a separate cable to a harness worn bythe person, permitting rotation of the blades about a common point relative to the person. Such harness may be provided for example with a journalled member to diametrically opterrain, without serious damage In launching objects from aircraft, the airfoil may be carried in racks within or without the aircraft and be pulled therefrom, as the object, whether bomb, packet, or person, is released from the aircraft and exerts a pull'tnrough the connecting cable.

It is of course possible, by disposing the C. G. of the wing assembly slightly back of the C. P. of ,the airfoil, to secure a position'pitching moment on the main airfoil requiring a lifting tail to stabilize the assembly at a position desired angle-of-atta'ck. Furthermore, such arrangement may use a tail stabilizer set at zero angle to the main airfoil. Under this condition,

and provided the air'foils are symmetrical sections, there results an assembly which is completely symmetrical as viewed for instance in Fig. 2.

Such an assembly when released in an airstream may start to spin in either direction and will function equally well regardless. Any nonsymmetrical arrangement, as for instance Fig. 2 as drawn, will fly in one direction only. That direction, for the form depicted in Figs. 1-9 is clockwise in the plane, while the direction for the form depicted in Figs. 10, 11, 12 is counterclockwise in plan.

The invention in its broader aspects is not limited to the specific mechanisms shown and described but departures may be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What I claim is:

1. An aerodynamic structure for lowering a load through the air said structure comprising an elongated airfoil device and flexible means adapted to connect said airfoil device to the load to be lowered, said airfoil device having generally spanwise alignment with said flexible connectlng means when lowering a load, said load and said airfoil device rotating as a unit on an axis intermediate said load and said airfoil device in load lowering operation, and said airfoil device being constructed and arranged and including means for normally maintaining it at a selected substantially constant angle-of-attack when lowering the load. a

2. An aerodynamic structure for lowering a load through the air, said structure comprising an elongated airfoil device including an elongated rigid airfoil blade member, a flexible cable secured to said rigid blade member at one :tip thereof and adapted to connect said blade member to the load to be lowered, said blade member having generally spanwise alignment with said cable when lowering a load,'said load and airfoil device being adapted to rotate as'a unit on a spin axis intermediate the" centers of mass of said load and said airfoildevice in load lowering operation, and said air-foil device being constructed and arranged and including means for normally maintaining said blade member at a-selected substantially constant angle-of-attack when lowering the load. I

3. An aerodynamic structure for lowering a load through the air said structure comprising an elongated airfoil device and flexible means adapted to connect said airfoil device to the load to be lowered, said airfoil device having generally spanwise alignment with said flexible connecting means when lowering a load, said load and said airfoil device rotating as a unit on an axis intermediate said load and said airfoil device in load lowering operation, and said airfoil device being constructed and arranged and including aero dynamic stabilising means for normally maintaining it at said selected constant angle-ofattack approximating its angle-of-attack' of maximum L/D when lowering the load, said stabilising means comprising a pivotally mounted airfoil member pivotalin one direction in response to the spanwise component of'centrifug'al force on said member in excess of a predetermined value for automatically varying the angleof-attack and hence diminishing the rotational speed of said airfoil device and means yieldably opposing said pivotal movement of said airfoil member for restoring said member to its original setting and thereby restoring said airfoil device to said selected constant an-gle-of-attack as said rotational speed diminishes and said spanwise component of centrifugal force diminishes to said predetermined value.

4. A device for retarding the progress of a load body through the atmosphere comprising, for connection to said body, an aerodynamic liftproducing structure possessing stability about its spanwise axis (longitudinal stability) so as .to meet the air at a stable (constant) angle-ofattack, said structure comprising an airfoil of foldable construction, an outrigger pivotally mounted on said airfoil, and a stabilizer pivotally mounted on said outrigger wherebysaid airfoil, stabilizer and outrigger may be folded into a compact unit for stowing and packing prior to use.

5. Thecombination with aload body of an aerodynamic lift-producing structure of foldable construction possessing stability about its spanwise axis (longitudinal stability) so as to meet the air at a stable (constant) angle of attack; a container in which said structure is removably lodged in a folded condition; a cable connecting said structure to said body; and, a separable band releasably securing said structure in said container and said container to said body.

6. A device for retarding the progress of a body through the atmosphere comprising an airfoil means for stabilizing said airfoil about its spanwise axis to meet the air at a stable (constant) angle-of-attack, said stabilizing means comprising a pivotally mounted stabilizer member, and means yieldably opposing pivotal movement of said stabilizer member in one direction; and, flexible means for connecting said airfoil to said object.

7. A device for retarding the progress of a body through the atmosphere comprising an airfoil; means for stabilizing said airfoil about its spanwise axis to meet the air at a stable (constant) angle-of-attack, said stabilizing means comprising a centrifugally responsive pivotally mounted stabilizer member, the pivot axis of said member being inclined to the span of said airfoil, and means yieldably opposing pivotal movement of said member in one direction; and, cable means for connecting said airfoil to said object.

SAMUEL DAVIS ROBINS. 

